Digital Modulation

ABSTRACT

The present application relates to embodiments of methods and a device for digital modulation. In a first embodiment of the method, the following steps are executed:
     determining a polarity of the signal,   providing an inverted carrier signal,   providing an inverted signal by an inversion of the polarity of at least one portion of the signal,   mixing the signal with the carrier signal when the signal has the first polarity, and   mixing the inverted signal with the inverted carrier signal when the signal has the second polarity.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from German Patent Application No.102008049666.9, which was filed on Sep. 30, 2008, and is incorporatedherein in its entirety by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a method and a device for a digitalmodulation.

A modulator is used for the modulation of a useful signal onto a carriersignal. A modulator is frequently used in transmission systems, like,for example, in wire-bonded or wireless communication systems.

In different communication systems, here different types of modulationare used for the modulation of information included in the useful signalonto the carrier signal. Examples for this are modulation types whichuse a phase modulation and/or an amplitude modulation.

In particular in a mobile communication system, like, e.g., a mobileradio system having a time-limited energy supply, it is here desirablefor the modulator to comprise a high power efficiency. Thus, a lowenergy consumption and thus a longer operation time of a correspondingterminal device may be achieved.

In particular in the field of mobile radio, a parallel propagation ofdifferent communication standards exists, like, e.g., of GSM, EDGE,UMTS, HSUPA, WLAN, Wimax, DECT, Bluetooth, etc. The same use differentmodulation types. In some standards the same are present in a combinedway to achieve higher bandwidths. It is accordingly possible to providemodulators which may execute a modulation for different communicationstandards. For example, high-frequency transmission devices exist whichmay execute both a GMSK modulation with a constant envelope of theoutput signal for a GSM mobile radio system and an 8-PSK modulation witha non-constant envelope for an EDGE mobile radio system.

Current solutions utilize a Cartesian modulator architecture or a polarmodulator architecture. They have the disadvantage, however, that theycomprise a high portion of analog circuit blocks. These disadvantages,compared to digital circuit blocks, are, for example, a greater errorand/or distortions by analog filter adaptations in the representation ofconstellation points of the modulation scheme used. Such deviations are,for example, indicated with the so-called error vector magnitude (EVM).By a direct current portion (DC offset) in signal processing, anincreased loss of the carrier signal results (carrier leakage). All inall, a higher power consumption thus results which is not wantedparticularly in mobile terminal devices.

When using analog circuit blocks, compared to digital circuit blocks agreater chip area is needed if the transmission device is arranged in anintegrated member. In this connection, additional problems result withthe scaling of circuit structures when using new, minimizedsemiconductor technologies.

It is thus desirable for a transmission device to comprise a highestpossible portion of digital circuit blocks or a high portion of switchedlogical blocks, respectively.

The present invention is based on the problem of providing a method fora power-efficient modulation and/or a power-efficient modulation device.

This object is achieved by the method having the features of patentclaim 1 and/or by the modulation device having the features of patentclaim 5.

The method for modulating a signal alternating between a first polarityand a second polarity onto a carrier signal comprises the followingsteps:

-   -   providing an inverted carrier signal,    -   determining a polarity of the signal,    -   mixing the signal with the carrier signal when the signal        comprises the first polarity, and    -   mixing the signal with the inverted carrier signal when the        signal comprises the second polarity.

The modulation device for modulating a signal alternating between afirst polarity and a second polarity onto a carrier signal comprises aninverter for providing an inverted carrier signal. Further, it comprisesa means for determining a polarity of the signal. Further, it comprisesa mixer cell which is coupled to the inverter and to the means and whichis implemented such that it mixes the signal with the carrier signalwhen the signal comprises the first polarity and that it mixes thesignal with the inverted carrier signal when the signal comprises thesecond polarity.

Different advantageous implementations and embodiments of the inventionresult from the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the invention is explained in more detail withreference to the accompanying drawings, in which:

FIG. 1 shows a first embodiment of a modulation device;

FIG. 2 shows an exemplary signal divider for application in the firstembodiment of FIG. 1;

FIG. 3 shows a second embodiment of a modulation device;

FIG. 4 shows an exemplary means for providing a unipolar signal for anapplication in the first embodiment of FIG. 3;

FIG. 5 shows a third embodiment of the modulation device;

FIG. 6 shows a Cartesian modulator with the inventive modulation device;

FIG. 7 shows a polar modulator with the inventive modulation device; and

FIG. 8 shows an embodiment of a method for modulating a signalalternating between a first polarity and a second polarity onto acarrier signal.

DETAILED DESCRIPTION OF THE INVENTION

All embodiments have in common that the illustrated modulation deviceseach modulate one signal onto a carrier signal.

The signal is a useful signal containing information. It is usuallypresent as a digital signal in the baseband and is modulated onto thecarrier signal by the modulation device. The carrier signal is a signalcentered around a carrier frequency. The carrier frequency usuallycorresponds to a center frequency of a transmission band of acommunication system. Usually, the carrier signal is generated by afrequency synthesizer, like, e.g. a controlled oscillator, aphase-locked loop or a ring oscillator.

FIG. 1 shows a first embodiment of a modulation device. The modulationdevice comprises a first input 100 for receiving a signal and a secondinput 102 for receiving a carrier signal. The first input 100 isconnected to a signal divider 104. The signal divider 104 divides thesignal according to a polarity of the signal into a first signalcomponent and a second signal component. The first signal component isprovided at a first signal divider output 106. The second signalcomponent is provided at a second signal divider output 108.

Here, the first signal component corresponds to the portion of thesignal comprising the first polarity, for example the case of a positivesignal level. The second signal component corresponds to the portion ofthe signal comprising the second polarity, for example the case of anegative signal level. Here, the signal divider 104 represents a meansdividing a signal alternating between two polarities into two signalcomponents, respectively corresponding to the portion of one of thepolarities. The original signal may be reproduced by a time-accurateoverlaying of the signal components.

In the illustrated embodiment, the signal is a digital signal. Thesignal divider 104 executes a digital signal processing and provides thefirst signal component and the second signal component in a digitalform.

The first signal divider output 106 is connected to a first input 112 ofa first mixer 114 via a first digital/analog converter 110. The firstdigital/analog converter 110 converts the first signal component into afirst analog signal component. A second input 116 of the first mixer 114is connected to the second input 102. In the first mixer 114, the firstanalog signal component is mixed onto the carrier signal, and thus afirst modulation component is provided.

The input 102 is further connected to the first input 120 of a secondmixer 122 via a first inverter 118. The second signal divider output 108is connected to a second digital/analog converter 126 via a digitalinverter 124. The second digital/analog converter 126 thus provides asecond analog signal component determined from the second signalcomponent by an inversion of the polarity and a subsequentdigital/analog conversion. It is obvious that the steps may be executedin any order to achieve the same result. The second digital/analogconverter 126 is coupled to a second input 128 of the second mixer 122to provide the second analog signal component to the same. In the secondmixer 122 the second analog signal component is mixed onto the invertedcarrier signal, and thus a second modulation component is provided. Asthe determination of the second analog signal component includes aninversion of the second signal component, the signal processing of thesecond mixer 122 corresponds to a modulation of the second signalcomponent onto the carrier signal.

The outputs of the first mixer 114 and the second mixer 122 are suppliedto the inputs of an adder 130 and overlaid there. In a simplerealization of the adder 130 a node is provided at which the outputs ofthe mixers are brought together. An output of the adder 130 is connectedto a signal output 132 of the modulation device.

The modulation device illustrated in FIG. 1 executes a modulation of thesignal onto the carrier signal by dividing the signal into two signalcomponents. The first signal component corresponds to the portion of thesignal comprising a first (e.g. positive) polarity. The second signalcomponent corresponds to the portion of the signal comprising a second(e.g. negative) polarity. The modulation is subsequently individuallyexecuted for each of the signal components. Subsequently, the separatelyprovided modulation components are combined. This technology thus uses aseparate signal processing according to the polarity of the signal. Inparticular, it is thus possible to apply a certain type of mixer in themodulation device. A signal component is supplied both to the firstmixer 114 and also to the second mixer 122 at one input, wherein thesignal component only comprises one polarity. Signal portions of theother polarity are processed in the other signal path. This allows theuse of a so-called “unipolar mixer cell”, and/or a single-sign mixercell for the first mixer 114 and the second mixer 122. Such a mixer cellis implemented to process a sign of the modulating signal in contrast toconventional mixer cells which may process both signs of the signal tobe modulated. By this, in particular a high efficiency may be achievedwhen mixing the signal component with the carrier signal.

FIG. 2 shows an exemplary signal divider for an application in the firstembodiment of FIG. 1. On the left side, FIG. 2 shows the symbol of asignal divider 104 with an input 100 for receiving the signal. A firstsignal component determined from the signal is provided at a firstsignal divider output 106. A second signal component determined from thesignal is provided at a second signal divider output 108. On the rightside, a schematical illustration of a block diagram of the setup of thesignal divider is represented.

The input 100 is connected to a first multiplexer input 200 of amultiplexer arrangement 202. It is further connected to a secondmultiplexer input 202 of the multiplexer arrangement 202. Finally, theinput 100 is connected to a means 206 for determining the polarity ofthe signal. The means 206 for determining the polarity of the signaldetermines the polarity of the signal. For the case of a digital inputsignal, it determines the sign of the signal value, which is usuallyseparately indicated by one bit. In this case, the determination of avalue of one bit from the digital word of the signal is sufficient. Themeans 206 for determining the polarity of the signal is connected to acontrol input 208 of the multiplexer arrangement 202 and switches themultiplexer arrangement 202 according to the determined polarity of thesignal.

The multiplexer arrangement 202 further comprises a third multiplexerinput 210 and a fourth multiplexer input 212. At the third multiplexerinput 210 and the fourth multiplexer input 212 a constant input signalis applied to which a zero value of the signal corresponds, i.e. a valueof the signal whose polarity is undetermined. This may, for example, bea zero level or a data word corresponding to zero. The constant inputsignal may, for example, be stored in a register and be readable fromthere. It is further possible that the constant input signal is providedby a mass and/or reference voltage terminal.

According to the polarity of the signal determined by the means 206, themultiplexer arrangement 202 connects the first signal divider output 106to the input 100 or the constant input signal. At the same time, themultiplexer arrangement 202 connects the second signal divider output108 to the constant input signal or to the input 100. Here, either thesignal is provided at the first signal divider output 106 and theconstant input signal at the second signal divider output 108 (firststate) or the constant input signal is provided at the first signaldivider output 106 and the signal at the second signal divider output108 (second state). In one possible implementation, the first state isassumed for the case of a positive polarity, i.e. a positive sign of thesignal, and the second state for the case of a negative polarity, i.e. anegative sign of the signal. It is thus achieved that, at the firstsignal divider output 106, the first signal component is provided withthe signal portion of a positive polarity, while at the second signaldivider output 108 the second signal component is provided with thesignal portion of a negative polarity.

For the case that the signal takes on an undetermined polarity, forexample the polarity determined last may further be assumed, as themultiplexer arrangement 202 provides correct output values in everystate at the first signal divider output 106 and the second signaldivider output 108.

FIG. 3 shows a second embodiment of a modulation device. The modulationdevice comprises a first input 100 for receiving a signal and a secondinput 102 for receiving a carrier signal. The first input 100 isconnected to a signal divider 300 (illustrated in dashed lines).

The signal divider 300 divides the signal according to a polarity of thesignal into a first signal component and a second signal component. Thefirst signal component is provided at a first signal divider output 106.The second signal components is provided at a second signal divideroutput 108.

Here, the first signal component corresponds to the portion of thesignal comprising the first polarity, e.g. the case of a positive signallevel. The second signal component corresponds to the portion of thesignal comprising the second polarity, e.g. the case of a negativesignal level. Here, the signal divider 300 represents a means dividing asignal alternating between two polarities into two signal componentswhich respectively correspond to the portion of one of the polarities.

In the illustrated embodiment, the signal is a digital signal. Thesignal divider 300 provides the first signal component and the secondsignal component in an analog form, however. In this respect, the signaldivider 300 comprises a first means 206 for determining the polarity ofthe signal which is connected to the input 100 so that the signal issupplied to the same. The first means 206 determines the polarity of thesignal. For the case of a digital input signal it determines the sign ofthe signal value, which is conventionally separately indicated by onebit. In this case, the determination of a value of one bit from thedigital word of the signal is sufficient.

The input 100 is further connected to a second means 302 for forming anabsolute value of the signal and/or for providing a unipolar signal fromthe signal. The signal is supplied to the second means 302 for formingan absolute value. In the second means 302 an output signal is providedrepresenting the absolute value of the signal. For the case of a digitalinput signal, it sets the sign of the signal value to a positive value.With regard to FIG. 4, a possible implementation of the second means 302is illustrated. Apart from that, a plurality of embodiments arepossible, for example in which the sign is truncated or set to a certainvalue in another form.

The output signal is supplied to a multiplexer arrangement 202 via adigital/analog converter 304. On the output side, the digital/analogconverter 304 is connected to a first multiplexer input 200 of amultiplexer arrangement 202. It is further connected to a secondmultiplexer input 202 of the multiplexer arrangement 202.

The means 206 for determining the polarity of the signal is connected toa control input 208 of the multiplexer arrangement 202 and switches themultiplexer arrangement 202 according to the determined polarity of thesignal.

The multiplexer arrangement 202 further comprises a third multiplexerinput 210 and a fourth multiplexer input 212. At the third multiplexerinput 210 and the fourth multiplexer input 212 a constant input signalis applied which corresponds to a zero value of the signal, i.e. a valueof the signal whose polarity is undetermined. This may, for example, bea zero level or a data word corresponding to a zero. The constant inputsignal may, for example, be stored in a register and be readable fromthere. It is further possible that the constant input signal is providedby a mass and/or reference voltage terminal.

According to the polarity of the signal determined by the first means206, the multiplexer arrangement 202 connects the first signal divideroutput 106 to the digital/analog converter 304 or the constant inputsignal. Simultaneously, the multiplexer arrangement 202 connects thesecond signal divider output 108 to the constant input signal or to thedigital/analog converter 304.

Here, either the signal is provided at the first signal divider output106 and the constant input signal at the second signal divider output108 (first state) or the constant input signal is provided at the firstsignal divider output (106) and the signal at the second signal divideroutput 108 (second state). In one possible implementation, the firststate is assumed for the case of a positive polarity, i.e. a positivesign of the signal, and the second state for the case of a negativepolarity, i.e. a negative sign of the signal. It is thus achieved thatat the first signal divider output 106 the first signal component withthe signal portion of a positive polarity is provided, while at thesecond signal divider output 108 the second signal component with thesignal portion of a negative polarity is provided.

For the case that the signal assumes an undetermined polarity, forexample the polarity determined last may further be assumed, as themultiplexer arrangement 202 at the first signal divider output 106 andthe second signal divider output 108 provides correct output values inevery state.

The first signal divider output 106 is connected to a first input 112 ofa first mixer 114. A second input 116 of the first mixer 114 isconnected to the second input 102. In the first mixer 114 the firstsignal component is mixed to the carrier signal and thus a firstmodulation component is provided.

The input 102 is further connected to the first input 120 of a secondmixer 122 via a first inverter 118. The second signal divider output 108is coupled to a second input 128 of the second mixer 122 to supply thesecond signal component to the same. In the second mixer 122 the secondsignal component is mixed to the inverted carrier signal and thus asecond modulation component is provided. Because the determination ofthe second signal component, by forming an absolute value, includes aninversion of the second signal component, the signal processing of thesecond mixer 122 corresponds to a modulation of the second signalcomponent onto the carrier signal.

The outputs of the first mixer 114 and the second mixer 122 are suppliedto the inputs of an adder 130 and are overlaid there. In a simplerealization of the adder 130 a node is provided at which the outputs ofthe mixers are brought together. An output of the adder 130 is connectedto a signal output 132 of the modulation device.

Compared to the embodiment illustrated in FIG. 1, the embodiment of FIG.3 comprises less components as a digital/analog converter may beomitted. It is here necessitated, however, to provide an absolute valueof the signal. As digital/analog converter architectures generallycomprise a power loss, the use of a digital/analog converter 304 has anadvantage with regard to energy efficiency.

FIG. 4 shows an exemplary means for providing a unipolar signal forbeing applied in the first embodiment of FIG. 3. On the right-hand side,FIG. 4 shows the symbol of means for providing a unipolar signal with aninput 400 for receiving the signal. A unipolar output signal determinedfrom the signal is provided at an output 402. On the left-hand side, aschematical illustration of a block diagram of the setup of the means isrepresented.

The input 400 is connected to a first multiplexer input 404 of amultiplexer arrangement 406. It is further connected to a secondmultiplexer input 408 of the multiplexer arrangement 406. Finally, theinput 400 is connected to a means 410 for determining the polarity ofthe signal. The means 410 determines the polarity of the signal. For thecase of a digital input signal, it determines the sign of the signalvalue which is usually indicated separately by one bit. In this case,the determination of one value of one bit from the digital word of thesignal is sufficient. The means 410 is connected to a control input 412of the multiplexer arrangement 406 and switches the multiplexerarrangement 406 according to the determined polarity of the signal.

The multiplexer arrangement 406 further comprises a third multiplexerinput 414 and a fourth multiplexer input 416. At the third multiplexerinput 414 and the fourth multiplexer input 416 a constant input signalis applied with corresponds to a zero value of the signal, i.e. a valueof the signal whose polarity is undetermined. This may, for example, bea zero level or a data word which corresponds to a zero. The constantinput signal may, for example, be stored in a register and be readablefrom there. It is also possible that the constant input signal isprovided by a mass and/or reference voltage terminal.

According to the polarity of the signal determined by the means 410, themultiplexer arrangement 406 connects a first multiplexer output 418 tothe input 400 or the constant input signal. Simultaneously, themultiplexer arrangement 202 connects a second multiplexer output 420 tothe constant input signal or to the input 400. Here, either the signalis provided at the first multiplexer output 418 and the constant inputsignal at the second multiplexer output 420 (first state) or theconstant input signal is provided at the first multiplexer output 418and the signal at the second multiplexer output 420 (second state). Inone possible implementation, the first state is assumed for the case ofa positive polarity, i.e. a positive sign of the signal, and the secondstate is assumed for the case of a negative polarity, i.e. a negativesign of the signal. It is thus achieved that, at the first multiplexeroutput 418, the first signal component is provided with the signalportion of a positive polarity, while, at the second multiplexer output420, the second signal component is provided with the signal portion ofa negative polarity.

For the case that the signal takes on an undetermined polarity, forexample the polarity determined last may further be assumed, as themultiplexer arrangement 202 at the first multiplexer output 418 and thesecond multiplexer output 420 provides correct output values in eachstate.

The first multiplexer output 418 is connected to a first input 422 of amultiplexer 424 and the second multiplexer output 420 is connected to asecond input 428 of the multiplexer 424 via an inverter 424. A controlinput 430 is connected to the means 410. The multiplexer 424 iscontrolled according to the polarity of the signal.

Thus, the signal at the output 402 is provided with a positive polarity,as such portions of the signal comprising a negative polarity are passedon to the output 402, inverted by the inverter 426.

The multiplexer 424 may be implemented as a simple switch.

FIG. 5 shows a third embodiment of the modulation device. The modulationdevice comprises a first input 100 for receiving a signal and a secondinput 102 for receiving a carrier signal. The modulated signal isprovided at an output 132.

The first input 100 is provided with a means 500 for providing aunipolar signal which may, for example, be implemented by the means ofFIG. 4. The means 500 generates a unipolar signal from the signal, inwhich portions with a negative polarity are inverted. It is connected toa first mixer input 504 of a mixer 506 via a digital/analog converter502. The mixer 506 may be implemented analog to the embodiments of FIG.1 and FIG. 3 as a single-sign mixer.

The first input 100 is further connected to a means 508 for determiningthe polarity of the signal. The means 508 for determining the polarityof the signal determines the polarity of the signal. For the case of adigital input signal it determines the sign of the signal value which isusually separately indicated by one bit. In this case, the determinationof a value of one bit from the digital word of the signal is sufficient.

The second input 102 is connected to a first multiplexer input 510 of amultiplexer 512. It is connected to a second multiplexer input 516 ofthe multiplexer 512 via an inverter 514. A multiplexer output 518 isconnected to a second mixer input 520 of the mixer 506. A control input522 of the multiplexer 512 is connected to the means 508.

A mixer output 524 is connected to the output 132.

The illustrated modulator uses the inventive principle by representingthe signal to be modulated as an absolute signal. This means that aunipolar signal is made from the signal by inverting the signal portionswhich comprise a negative polarity. The unipolar signal is selectivelyapplied onto the carrier signal or the inverted carrier signal with thehelp of the multiplexer 512. Here, the unipolar signal is applied to thecarrier signal when the signal comprises a positive polarity, and it isapplied to the inverted carrier signal when the signal comprises anegative polarity. At the output, thus a phase- and sign-corrected,modulated signal is provided.

In contrast to the embodiments of FIG. 1 and FIG. 2, the embodiment ofFIG. 5 does not divide the signal into two portions, whereby errorsregarding run-time differences are reduced. Additionally, a low-effortand efficient circuit results.

FIG. 6 shows a Cartesian modulator with the inventive modulation device.The modulator comprises a first input 600 for receiving an in-phasecomponent of a useful signal, a second input 602 for receiving aquadrature component of a useful signal and a carrier signal input 604.

The first input 600 is connected to a signal input 606 of a firstmodulation device 608. The first modulation device 608 is an inventivemodulation means and may, for example, be implemented by one of theimplementations of FIG. 1, FIG. 3 or FIG. 5.

The second input 602 is connected to a signal input 610 of a secondmodulation device 612. Also the second modulation device 608 is aninventive modulation means and may, for example, be implemented by oneof the implementations of FIG. 1, FIG. 3 or FIG. 5.

The carrier signal input 604 is connected to a carrier signal input 616of the first modulation device 608 and a carrier signal input 618 of thesecond modulation device 612 via a phase shifter 614. The phase shifter614 provides the carrier signal in a phase-corrected manner at thecarrier signal input 616 of the first modulation device 608 and shiftedby a phase of 90° at the carrier signal input 618 of the secondmodulation device 612.

An output 620 of the first modulation device 608 and an output 622 ofthe second modulation device 612 are connected to a modulator output 626via an adder 624.

The illustrated modulator represents a conventional Cartesian modulatorin which the mixers are, however, replaced by an inventive modulationdevice.

FIG. 7 shows a polar modulator comprising the inventive modulationdevice. The polar modulator comprises an input 700 for receiving auseful signal. The useful signal is present in a digital form and is,for example, provided by a base band-processing unit and/or amicroprocessor or another digital signal processing unit. The input 700is connected to a digital modulator 702. The digital modulator 702executes a digital modulation and possibly a pulse shaping of the usefulsignal. The modulation here includes both a phase modulation and also anamplitude modulation of the useful signal. The digital modulator 702provides a phase signal at a first modulator output 704 which containsphase information of the modulated useful signal. At the secondmodulator input 706, amplitude information of the modulated usefulsignal is provided.

The first modulator output 704 is connected to a detector 706, whichprovides, for the case of a phase leap of about 180° at a detectoroutput 708 a sign signal with the value “−1”. In all other cases, thedetector provides a sign signal with the value “+1” at the detectoroutput 708.

The detector 706 further supplies the phase signal to a phase modulator710. The phase modulator 710 provides a carrier signal modulateddepending on the phase signal at a phase modulator output 712, whereinthe signal is supplied to a second input 102 of a modulation device 714.The modulation device 714 is an inventive modulation means and may, forexample, be implemented by one of the implementations of FIG. 1, FIG. 3or FIG. 5.

The second modulator output 706 is connected, via a multiplier 716, to adigital/analog converter 718 which is in turn connected to a first input100 of the modulation device 714 via a low pass filter 720.

The multiplier 716 is connected to the detector output 708 and receivesthe sign signal to multiply the same with the amplitude signal. The thuscorrected amplitude signal is converted into an analog amplitude signalin the digital/analog converter 718. After a filtering in the low passfilter 720, the thus processed amplitude signal is modulated in themodulation device to the phase-modulated carrier signal and provided atan output 132 of the polar modulator.

The illustrated embodiment of the polar modulator is especially suitablefor a transmission system in which phase leaps close to 180° exist. Forexample, this is the case in a UMTS system. As such phase leaps oftenrepresent difficulties in phase modulation, it is advantageous toconsider the phase leap with the amplitude signal and have the phasemodulator 710 accordingly not execute phase leaps of approx. 180°.

FIG. 8 shows an embodiment of a method for modulating a signalalternating between a first polarity and a second polarity onto acarrier signal.

In a first step 800 an inverted carrier signal is provided.

In a second step 802 a polarity of the signal is determined.

In a third step 804 the signal is mixed with the carrier signal when thesignal comprises the first polarity, and in a fourth step 806 the signalis mixed with the inverted carrier signal when the signal comprises thesecond polarity.

The sequence of the steps is here randomly interchangeable as far assteps 800 and 802 are executed before steps 804 and 806.

While this invention has been described in terms of several embodiments,there are alterations, permutations, and equivalents which fall withinthe scope of this invention. It should also be noted that there are manyalternative ways of implementing the methods and compositions of thepresent invention. It is therefore intended that the following appendedclaims be interpreted as including all such alterations, permutationsand equivalents as fall within the true spirit and scope of the presentinvention.

1. A method for modulating a signal alternating between a first polarityand a second polarity onto a carrier signal, comprising: determining apolarity of the signal, providing an inverted carrier signal, providingan inverted signal by an inversion of the polarity of at least oneportion of the signal, mixing the signal with the carrier signal whenthe signal comprises the first polarity, and mixing the inverted signalwith the inverted carrier signal when the signal comprises the secondpolarity.
 2. The method according to claim 1, comprising: providing afirst partial signal corresponding to the signal portion of the signalcomprising the first polarity, and providing a second partial signalcorresponding to the inverted signal portion of the signal comprisingthe second polarity.
 3. The method according to claim 2, comprising:mixing the first partial signal with the carrier signal, and mixing thesecond partial signal with the inverted carrier signal.
 4. The methodaccording to claim 1, comprising: providing a unipolar signal from thesignal, mixing the unipolar signal with the carrier signal when thesignal comprises the first polarity, and mixing the unipolar signal withthe inverted carrier signal when the signal comprises the secondpolarity.
 5. A modulation device for modulating a signal alternatingbetween a first polarity and a second polarity onto a carrier signal,comprising: an inverter for providing an inverted carrier signal, ameans for determining a polarity of the signal and a mixer coupled tothe inverter and the means which is implemented such that it mixes thesignal with the carrier signal when the signal comprises the firstpolarity and that it mixes the signal with the inverted carrier signalwhen the signal comprises the second polarity.
 6. The modulation deviceaccording to claim 5, wherein the mixer comprises a mixer cell.
 7. Themodulation device according to claim 5, wherein the mixer comprises aswitching element controlled by the means.
 8. The modulation deviceaccording to claim 5, wherein the mixer comprises a signal dividerproviding a first partial signal and a second partial signal, whereinthe first partial signal corresponds to the signal portion of the signalwith the first polarity and the second partial signal corresponds to theinverted signal portion of the signal with the second polarity.
 9. Themodulation device according to claim 5, wherein the mixer comprises ameans for providing a unipolar signal from the signal.
 10. Themodulation device according to claim 5, which is arranged in a Cartesianmodulator.
 11. The modulation device according to claim 5, which isarranged in a polar modulator.